Auto merge of #1139 - gnzlbg:map_anon, r=gnzlbg
Auto merge of #1139 - gnzlbg:map_anon, r=gnzlbg

Add alias for MAP_ANONYMOUS to Apple targets.

Closes #1060 .

rust-lang/libc,rust-lang/libc,rust-lang-nursery/libc,rust-lang-nursery/libc,rust-lang/libc,rust-lang-nursery/libc